SKM 2021 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 16: Semiconductors: Optical, Transport and Ultrafast Properties

HL 16.2: Talk

Thursday, September 30, 2021, 11:30–11:45, H1

Kerr and Faraday rotations of two-dimensional topological flat bands — Alireza Habibi, Johan Ekström, Thomas Schmidt, and •Eddwi Hasdeo — Department of Physics and Materials Science, University of Luxembourg, Luxembourg, Luxembourg

Flat-band systems are one of main subjects of research in condensed-matter physics especially after the discovery of a strongly correlated phase in twisted bilayer graphene. Flat bands can be observed directly via angle-resolved photo-emission spectroscopy. However, due to the band flatness and the close proximity to the Fermi energy, a flat band is usually difficult to characterize. Here, we propose an alternative characterization method for topological flat bands using photon absorption. In topological bands, the anomalous Hall conductivity can rotate the incident light polarization, resulting in a rotated polarization of the transmitted light (Faraday effect) and the reflected light (Kerr effect). In this work, we employ a model featuring nearly flat bands, for which the bandwidth is much smaller than the band gap. We investigate the dynamical (ac) conductivities of the model in the presence of an external electric field. We contrast how flat bands and dispersive bands can be detected sensitively via Kerr and Faraday rotations. These results can serve as a simple characterization tool to determine the bandwidth or band flatness of topological materials.